…rebuttals are unwise, argue Derek Rucker and David Dubois, of the Kellogg School of Management, and Zakary Tormala, of Stanford business school, three psychologists. By restating the rumours, Coke helps to propagate them. Its web page is a magnet for search engines. And people who read rebuttals tend to forget the denial and remember only the rumour, says Mr Rucker.

As information is passed around, important qualifiers are lost. A rumour may start as “I’m not sure if this is true, but I heard that…” Then it evolves into: “I heard that…” Finally it becomes: “Did you know that…?” Even when no one intends to spread falsehoods, they spread.

…if your starting point is obscurity, even bad publicity may be helpful, argues Alan Sorensen, an economics professor at Stanford University’s Graduate School of Business. He looked at the effect of book reviews in the New York Times. In a study published inMarketing Science*, he found that well-known authors who earned glowing reviews for a new book could expect to sell 42% more copies, whereas a negative review caused sales to drop by 15%. For unknown authors, however, it did not matter whether a book was panned or lauded. Simply being reviewed in the Times bumped up sales by a third.

Mr Sorensen extrapolated his findings to other businesses. For small brands fighting for recognition in crowded markets, almost any publicity is beneficial, he reckons. One reason is that, for lesser-known brands, negative perceptions fade more quickly in consumers’ minds than their general awareness of the product.